1. Technical Field
The present invention relates to a projector and a projection system.
2. Related Art
A projector adapted to 3D that realizes stereoscopic video display using a discharge lamp such as a high pressure mercury lamp has been put to practical use. In one system of the projector adapted to 3D, input signals are divided into a signal for left eye and a signal for right eye and sequentially alternately sent to alternately project a video for left eye and a video for right eye. An observer wears active shutter glasses, in which two shutters are alternately opened and closed, and selectively views the video for left eye and the video for right eye respectively with the left eye and the right eye. Consequently, the observer recognizes a video, which the observer is viewing, as a stereoscopic video. However, when the observer wears the active shutter glasses, a video entering the eyes of the observer is blocked by the shutters in a period substantially half of a viewing period. Therefore, the video is darkened.
To solve this problem, there have been proposed projectors that adopt a system for dimming the discharge lamp in synchronization with the active shutter glasses (see, for example, JP-A-2012-32504 (Patent Literature 1) and JP-A-2012-129049 (Patent Literature 2)). The projectors perform a diming operation for increasing the luminance of the discharge lamp when the shutters of the glasses are opened and reducing the luminance of the discharge lamp when the shutters are closed. When such dimming is performed, it is possible to increase the luminance during the opening of the shutters by the decrease in the luminance during the closing of the shutters without changing average luminance of the discharge lamp. Consequently, the observer can visually recognize a bright video.
However, in the projector disclosed in Patent Literature 1, when such a dimming operation is cyclically repeated, protrusions formed at the distal ends of electrodes of the discharge lamp are sometimes deformed. This is considered to be because, when a period for reducing the luminance of the discharge lamp is cyclically present, supplied power to the discharge lamp is partially insufficient and melting of the electrodes is suppressed. This is because the protrusions are formed when the distal ends of the electrodes are moderately melted. In projectors in recent years, an alternating current is supplied to the discharge lamp in most cases. In the projector disclosed in Patent Literature 1, since the dimming operation is synchronized with a video signal, the frequency of the alternating current applied to the discharge lamp is considerably high. Therefore, an anode operation time is short and the distal ends of the electrodes are less easily heated. Consequently, when the deformation of the protrusions increases, the life of the discharge lamp decreases.